5,224 research outputs found
Probing cosmological parameters with GRBs
In light of the recent finding of the narrow clustering of the
geometrically-corrected gamma-ray energies emitted by Gamma Ray Bursts (GRBs),
we investigate the possibility to use these sources as standard candles to
probe cosmological parameters such as the matter density Omega_m and the
cosmological constant energy density Omega_Lambda. By simulating different
samples of gamma-ray bursts, based on recent observational results, we find
that Omega_m (with the prior Omega_m + Omega_Lambda = 1) can be determined with
accuracy ~7% with data from 300 GRBs, provided a local calibration of the
standard candles be achieved.Comment: 4 pages, 2 figures, to appear in the Proceedings of the Conference
"30 Years of GRB Discovery", Santa Fe, New Mexico, USA, September 8-12, 200
Gamma-Ray Astronomy around 100 TeV with a large Muon Detector operated at Very High Altitude
Measurements at 100 TeV and above are an important goal for the next
generation of high energy gamma-ray astronomy experiments to solve the still
open problem of the origin of galactic cosmic rays. The most natural
experimental solution to detect very low radiation fluxes is provided by the
Extensive Air Shower (EAS) arrays. They benefit from a close to 90% duty cycle
and a very large field of view (about 2 sr), but the sensitivity is limited by
their angular resolution and their poor cosmic ray background discrimination.
Above 10 TeV the standard technique for rejecting the hadronic background
consists in looking for "muon-poor" showers.
In this paper we discuss the capability of a large muon detector (A=2500 m2)
operated with an EAS array at very high altitude (>4000 m a.s.l.) to detect
gamma-ray fluxes around 100 TeV. Simulation-based estimates of energy ranges
and sensitivities are presented.Comment: 4 pages, proceedings of the 30th ICRC, Merida, Mexico, 200
Identification of Showers with Cores Outside the ARGO-YBJ Detector
In any EAS array, the rejection of events with shower cores outside the
detector boundaries is of great importance. A large difference between the true
and the reconstructed shower core positions may lead to a systematic
miscalculation of some shower characteristics. Moreover, an accurate
determination of the shower core position for selected internal events is
important to reconstruct the primary direction using conical fits to the shower
front, improving the detector angular resolution, or to performe an efficient
gamma/hadron discrimination. In this paper we present a procedure able to
identify and reject showers with cores outside the ARGO-YBJ carpet boundaries.
A comparison of the results for gamma and proton induced showers is reported.Comment: 4 pages, to be published in the Proceedings of the 28th International
Cosmic Ray Conference (Tsukuba, Japan 2003
Expected sensitivity of ARGO-YBJ to detect point gamma-ray sources
ARGO-YBJ is a full coverage air shower detector currently under construction
at the Yangbajing Laboratory (4300 m a.s.l., Tibet, China). First data obtained
with a subset of the apparatus will be available in summer 2003 while the full
detector operation is expected in 2005. One of the main aims of ARGO-YBJ is the
observation of gamma-ray sources, at an energy threshold of a few hundreds GeV.
In this paper we present the expected sensitivity to detect point gamma ray
sources, with particular attention to the Crab Nebula. According to our
simulations a Crab-like signal could be detected in one year of operation with
a statistical significance of 10 standard deviations, without any gamma/hadron
discrimination.Comment: 4 pages, 2 Postscript figure
Treatment conditions and biochemical processes influencing seed priming effectiveness
A review of the scientific literature indicates osmotic priming (osmopriming) as the principal method of seed priming and polyethylene glycol (PEG) as the principal osmotic agent. An analysis of the available data across experiments carried out with different species under varying conditions showed an average 11% increase in percent germination and 36% shorter mean germination time (MGT) in primed vs. unprimed seeds. Moreover, in primed seeds MGT was less dependent on temperature, which is consistent with the effects expected from the treatment. Priming effects are mainly influenced by osmotic potential, temperature and time; major biochemical processes (repair of damaged DNA and RNA, preparation for cell division and increased antioxidant activity) are involved in treatment effects to an extent which is not fully ascertained in literature. A reduction of seed storage life is the major disadvantage of priming and the principal constraint to its diffusion, since dehydration to the initial moisture (drying-back) is needed to allow seed storage. Seed behaviour during drying-back, the role of the raffinose family oligosaccharides in cell membrane integrity and the expression of antioxidant enzymes in germinating seeds need to be further elucidated in a sufficient number of species, to promote a more reliable use of this technique
Feasibility of Tsunami Early Warning Systems for small volcanic islands
Abstract. This paper investigates the feasibility of Tsunami Early Warning Systems for small volcanic islands focusing on warning of waves generated by landslides at the coast of the island itself. The critical concern is if there is enough time to spread the alarm once the system has recognized that a tsunami has been generated. We use the results of a large scale physical model experiment in order to estimate the time that tsunamis take to travel around the island inundating the coast. We discuss how and where it is convenient to place instruments for the measurement of the waves
Lidar in Space Technology Experiment correlative measurements by lidar in Potenza, southern Italy.
An intensive lidar measurement campaign was carried out in Potenza (40°36′N-15°44′E, 820 m above sea level (asl)) in conjunction with the Lidar in Space Technology Experiment (LITE) mission and primarily aimed at the validation of LITE stratospheric aerosol measurements. Potenza lidar measurements in coincidence with all five nighttime overpasses near southern Italy (September 11, 12, 17, and 18, 1994) are compared with simultaneous LITE data. Potenza lidar data appear to be highly correlated with LITE data both at 355 and 532 nm. Potenza lidar versus LITE measurements of the aerosol-scattering ratio show a correlation coefficient of 0.72–0.81 at 355 nm and 0.88–0.93 at 532 nm, with an average calibration coefficient of 0.92 ± 0.19 at 355 nm and 1.02 ± 0.07 at 532 nm. Comparisons are also made in terms of the average Angstrom coefficient, whose values are consistent with submicrometer aerosol particles. Finally, Potenza lidar measurements of the aerosol layer base and top heights, the peak aerosol-scattering ratio and peak height, as well as of the aerosol scattering ratio at the cloud base appear to be consistent with measurements performed by other ground lidar stations in Europe during the LITE campaign as well as with the LITE data
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